Recently, the market for mobile devices such as mobile phones, PDAs, has been growing enormously. The diversity in functionalities and user interface has also been increased.
Existing mobile devices usually have a display (for example a Liquid Crystal Display) including a cursor which is to be controlled. The control of the cursor on the display is often performed by a 5-way joystick, which contains five switches located under the dome of a knob which can be operated by the user for performing any desired movement of the cursor. By pressing the joystick up or down or to the left or right, one of the four switches is closed, and this causes a corresponding movement of the cursor on the display in steps to a desired direction or position. With this kind of joystick and the use of four of the five switches only control of the cursor in four directions is possible. The fifth switch is usually provided as a central switch and is used for the “click” function, which means that the user can operate a corresponding button associated to the fifth switch to select a certain item on a menu by clicking the knob of the joystick vertically to thereby close the fifth switch.
PDAs and mobile phones nowadays have increasingly larger displays, and the control menus of such devices become more and more complex. Some specific functions such as gaming, web browsing, navigation, etc. may need a more precise and, thus, a continuous control of the cursor rather than a stepped control. Moreover, the mobile devices in question must be compact, robust, must have low power consumption and also a low price. With the joystick for such a mobile device it should be possible to perform the press-to-select function (that is, the “click” function), which means that a certain item in the menu can be selected by simply pressing the knob vertically.
Prior art documents, such as reference U.S. Pat. No. 6,326,948, disclose analogue joysticks which are based on optical principles. A common way of signal detection of those devices is that they detect the movement of a light spot with respect to a corresponding photodetector configuration. More precisely, the detection is based on the difference in the light coverage of the light spot upon the photodetectors. In this way, the area encircling the photodetectors must be rather large, depending upon the geometry of the device parts.
The click function mentioned in reference U.S. Pat. No. 6,326,948 B1 uses an aperture in between a light source for providing illumination light and a mirror for reflecting the illumination light, and the aperture adds complication to the alignment of the device and is disadvantageous in view of the dimensions thereof. The click function can also be provided by using a separate set of detectors only for this function.
Further details about the prior art briefly mentioned will be explained in detail hereinafter.
Regarding reference U.S. Pat. No. 6,326,948 B1, this document discloses an input device which consists of a base having a slide surface, a movable body which is slidable on the slide surface, a light-emitting element for emitting light, a reflective portion which is arranged on the movable body and which has a reflective surface for reflecting the light emitted by the light-emitting element, as well as a plurality of light receiving elements for receiving light which is reflected by the reflective portion.
More specifically, the light coming from the light emitting element is incident on the reflective portion and is reflected to create a light spot on the base. The light spot covers partly the light receiving elements. For operation by a user the movable body slidable on the slide surface has a recessed or hollow portion to be touched and operated by the user's finger. That is, during operation, the user puts his fingers on the movable body to which the reflective portion is fixed, and with the sliding movement of the movable body the reflective portion will slide on the slide surface and will make the light spot on the light receiving elements to move in a corresponding manner. The movement of the light spot will make some difference in the light coverage on the light receiving elements, so that as a result different signals can be observed at the output of the light receiving elements. By means of a subtraction method the signals corresponding to the movement of the movable body and, thus, of the reflective portion in the X-Y-plane can be obtained.
The input device according to reference U.S. Pat. No. 6,326,948 B1 further includes an elastic structure in conjunction with the movable body (which is slidable on the slide surface), so that a movement perpendicular to the X and Y plane is possible and, thus, a detection in the Z-axis can be performed.
A corresponding situation is shown in FIG. 6 depicting the arrangement of the light receiving elements PD1 to PD4 and the light emitting element located in the central portion of this arrangement.
Regarding the detection of a movement of the reflective portion in the X-Y-plane, it is to be noted that the light spot created on the light receiving elements (photodetectors) by the light emitting element and the reflective surface on the movable body has a distinct boundary, and the boundary of the light spot needs to run across the light receiving elements PD1 to PD4 during the operation corresponding to a movement of the user's finger with the slidingly supported movable body. It is hereby supposed that the irradiance of the light spot is homogeneous over the entire area of the light spot. Specifically, the dimensions of the light spot are limited according to the following inequality:d≦x≦2r+2lmax,  (1)in which d is the distance between two adjacent light receiving elements, x is the diameter of the light spot, r is the radius of the circle encircling the plurality of the light receiving elements, and lmax is the maximum movement distance of the movable body from the center.
The above inequality can be interpreted in the following way. Due to the reflection rule the maximum movement distance of the light spot on the base from the center is lmax′=2 lmax. Hence, inequality (1) can be rewritten asd≦x≦2r+lmax′  (2)
According to these considerations, the light spot diameter should be sized in such a way that the border of the light spot sweeps over the light receiving element areas covering the light receiving elements PD1 to PD4 when the movable body and in conjunction therewith the reflective portion moves during operation by the user. The inequalities (1) and (2) also imply that the light spot at the initial portion should cover partly the light receiving element areas, as is shown in FIG. 7. That is, the light spot covering partly the light receiving element areas and representing the initial position is represented by a dashed circle, whereas during operation, when the reflective portion slidingly moves, the boundary of the light spot should sweep across the light receiving elements (represented by a solid line circle in FIG. 7. The corresponding movement has, for example, been caused by the user in the X-direction, that is, to the right-hand side in FIG. 7.
The restriction according to the inequalities (1) and (2) has some disadvantages.
On the one hand, the inequalities (1) and (2) imply that the size of the area of the base B which contains the plurality of light receiving elements PD1 to PD4 should be larger than the light spot. However, the size of the light spot which is guided by the reflecting portion is determined by the reflector size and also the size of the light emitting element. Because those sizes cannot be made very small (or it is at least difficult or costly to make it small), the light spot size cannot be small, and this leads to a minimum size requirement for the substrate (base B) that contains the light receiving elements PD1 to PD4. Consequently, it is difficult to miniaturize the device, and the cost of the device is high due to the large sized substrate.
On the other hand, based on the inequalities (1) and (2), the size of the light receiving elements W (FIG. 6, the size indicated in light receiving element PD2) should be larger than a certain value which depends on the other geometries in order to ensure the proper operation:w≧x/(2√{square root over (2)})−d/2−lmax′/(2√{square root over (2)})  (3)wherein the dimension of d which represents the distance between the edge of two light receiving elements is shown in FIG. 6.
It is further to be noted that the above condition is not related to the minimum area needed for each light receiving elements PD1 to PD4 to get a readable electrical signal. Inequality (3) has been derived from inequality (1) and from the relation between d, W and r in FIG. 6.
Consequently, the substrate area in between the light receiving elements PD1 to PD4 cannot be maximized for other purposes like integration of electronics for control and signal processing.
For the detection of the Z-direction, which corresponds to the “click” function (also called the press-to-select function), the user of the input device can press the joystick vertically to chose a certain desired item on the display. In this case, the detection of a movement in the Z-direction can be performed by using the aperture which is located in between the reflector R and the light emitting element LD. This is shown in FIG. 8.
When the user intends to operate the click function the user vertically presses the elastic structure of the movable object such as a button so that the reflecting portion for reflecting the light of the light emitting element follows the vertical movement, and as a result the light spot size will increase which makes the total signal to increase, and on the basis of this modification of the light spot size the pressing action can be detected. A corresponding situation is shown in FIG. 8.
It is to be noted that this principle has some disadvantages. The use of the aperture makes the construction of the device more complicated and increases the dimensions thereof. The use of the aperture makes it necessary to align the aperture very well with respect to the reflector and the other elements of the input device which makes a proper setting of a total device more complicated. Furthermore, the aperture constitutes an additional component of the input device which will cause higher manufacturing and assembling costs.
In conventional input devices joysticks may basically have the principle according to reference U.S. Pat. No. 6,326,948 B1, but some modifications may be provided.
During operation, that is, under a force from the user's finger, the reflecting portion (reflector) may tilt a few degrees around a fixed rotation point, rather than sliding on the sliding surface of the movable body. This would cause an additional change in the size and position of the light spot and, thus, an additional change in the signal which is used for further data evaluation of the joystick movement.
Moreover, in a similar manner as in the reference discussed above, the size of the reflecting portion R, the distance between the light emitting element LD and the reflecting portion R, and the dimensions of the detectors PD1 to PD4 may be chosen such that the light spot LS covers approximately half of the area of the detecting elements PD1 to PD4, the arrangement of which is shown in FIG. 9 having Figure portions 9a and 9b. 
The principle is also based on the movement of the boundary of the light spot LS across the area of the light receiving elements. A disadvantage may occur in that the area which contains the light receiving elements cannot be made small, and the length of the light receiving elements in the radial direction cannot be made short and should depend on the geometry of the other components of the joystick.
At least the light receiving elements PD1 to PD4 and the corresponding electronics (electronic devices for data evaluation) can be integrated on a same substrate, such as a Si-substrate. The light emitting element LD which functions as the light source can be integrated on the same substrate, or can be mounted on the substrate as a separately manufactured component. The device can therefore have more degree of integration. The arrangements of the light receiving elements according to reference U.S. Pat. No. 6,326,948 B1 are discrete components mounted or molded on the base B.
In an alternative approach the light receiving elements can be divided up into a plurality of small elements so that a “discrete” way of detecting the signal can be used.
The detection of an operation in the Z-direction which corresponds to the click function can be done by having a plurality of light receiving elements which are always located inside the light spot. These light receiving elements are exclusively used for the detection in the Z-direction but not for any detections in the X- and Y-directions. Many ways of constructing the devices can be considered, such as based on Si photodiodes using CMOS, integrated with electronics, light emitting elements (light source) using light emitting diodes LED die or OLED, LTPS photodiodes with OLED light source, the light source being made from avalanche effect in CMOS circuit, etc.